The research project involves identifying susceptibility loci for IBD through genome-wide screening of affected relative pairs using non- parametric linkage analysis and gene identification through a variety of approaches. Unique aspects of the genetics of inflammatory bowel disease include the overlap between Crohn's disease and ulcerative colitis and its high prevalence in Ashkenazi Jews. Data on putative loci on chromosomes 16 and 12 are provided. Strategies for fine localization of loci, including fine-mapping by linkage disequilibrium, are proposed. alternative approaches to gene identification and mutation detection are discussed.